Hi Mario,
The AP needs the username/password that must be configured while the AP is connected to the WLC If no username/password was configured via the WLC this command is not available.
If the LWAPP AP did have the username and password changed while the LAP was joined to the controller then this is available via the AP's console connection
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Note This command requires the controller configured Enable password to enter the CLI EXEC mode.
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clear lwapp private-config
From this Troubleshooting doc;
http://www.cisco.com/en/US/docs/wireless/access_point/1130/installation/guide/113h_c4.html#wp1091061
setting of a Username/Password on an LWAPP AP becomes a valuable step in the configuration process;
Resetting the LWAPP Configuration on a Lightweight AP (LAP)
http://www.cisco.com/en/US/products/hw/wireless/ps430/products_tech_note09186a00808e2d27.shtml
Deleting the LWAPP Configuration File to Redeploy the AP
When you redeploy an access point after moving it from one location to another, you must first delete the LWAPP configuration file and restore the access point to the factory default settings. Deleting the LWAPP configuration enables the commands on the access point console to configure the static IP address on the access point, the IP address on the controller, the access point hostname, and the default gateway IP address.
To delete the LWAPP configuration and restore the factory defaults, enter the following command in EXEC mode on the access point console:
clear lwapp private-config
The clear lwapp private-config command becomes available on the access point console after the controller pushes a new username and password to the access point.
http://www.cisco.com/en/US/docs/wireless/access_point/conversion/lwapp/upgrade/guide/lwapnote.html#wp169479
Hope this helps!
Rob
